Sealing below shower tray.

[MikeSharp01]

Have to fit the waste to our daughters shower tray. The waste instructions, and its construction, want the rubber seal below the tray but the tray is not smooth. It is some sort of synthetic material and full of bubbles. Any thoughts on what I can use to fill the holes and then grind flat or is there a simpler solution? Once this goes in there will be no access except from above the tray so it needs to be right first time. 

[Vijay]

CT1?

[tonyshouse]

I would use a two part resin car bony type filler and fill all the air bubble holes under where the rubber washer goes and sand flat first, then rubber washer will do it’s job ok 

[MikeSharp01]

Thanks chaps look at both options. 

[Vijay]

if you do use CT1 or another adhesive sealant, I'd be tempted to leave the holes so the sealant has something to ooze into and fill the holes/won't come off. Then put the washer on while it's wet. Maybe clean everything with IPA first

[TonyT]

No plumber would be using car body filler,

buy a good quality silicone.

[SteamyTea]

Hard to tell, but usually it is a filled polyester resin used to cast these.

So a polyester car body filler would work fine.

Then CT1 @pocster's favourite, o  the fittings.

[Temp]

+1 to filling the holes with a polyester car body filler (sets quick so work fast). Sand smoth and use ct1.